Substantia nigra hyperechogenicity in essential tremor and Parkinson's disease: a longitudinal study

Background and purpose Essential tremor ( ET ) and Parkinson's disease ( PD ) sometimes overlap in their clinical expression with ET preceding PD onset, often leading to misdiagnosis. Transcranial sonography ( TCS ) has been shown to be a valid and non‐invasive diagnostic tool to identify early idiopathic PD and to differentiate it from ET . The purpose of this study was to investigate the relevance of substantia nigra hyperechogenicity in patients with ET . Methods A total of 138 patients (79 with PD , 59 with ET ) and 50 matched controls underwent TCS examination at baseline. All patients were followed in a 3‐year longitudinal assessment. Results A total of 10 subjects were excluded from the analysis due to the bilateral absence of a temporal acoustic window. During the follow‐up period, 11 of the patients with ET developed new‐onset parkinsonian features, without fulfilling criteria for PD diagnosis ( ET +). Nine patients developed clinical features meeting diagnostic criteria for probable PD ( ET ‐ PD ). Patients with ET − did not develop parkinsonian features. For each group, the maximum size of the substantia nigra hyperechogenicity was as follows: 5.62 ± 5.40 mm 2 in the control group, 19.02 ± 14.27 mm 2 in patients with PD , 9.15 ± 11.26 mm 2 in patients with ET −, 20.05 ± 13.78 mm 2 in patients with ET + and 20.13 ± 13.51 mm 2 in patients with ET ‐ PD . ET ‐ PD maximum values were significantly different from controls. Maximum values in patients with ET + were different from both controls and patients with ET −. Conclusion Substantia nigra hyperechogenicity in ET seems to represent a risk marker for developing early parkinsonian symptoms or signs in the 3 years following TCS assessment.